The present invention relates to a method for preparing (Z,Z,E)-7,11,13-hexadecatrienal, which is a sex pheromone substance of the citrus leafminer, a pest of citrus, by using (Z,Z,E)-1-chloro-6,10,12-pentadecatriene.
The citrus leafminer (Phyllocnistis citrella) is an important pest of citrus. It is parasitic and causes damage in young leaves and thereby has a serious influence on the growth of nursery trees. Its feeding damage marks accelerate occurrence of citrus canker. This pest mines the undersurface of leaves so that it cannot be controlled easily by pesticides. Its resistance to pesticides is also observed. Biological control methods have therefore been attracting attentions and a method of using a sex pheromone substance is expected as one of them.
It has been identified (W. S. Leal et al., J. Chem. Ecol. 32(1), 155-168 (2006)) that the sex pheromone composition of the citrus leafminer contains (Z,Z,E)-7,11,13-hexadecatrienal, (Z,Z)-7,11-hexadecadienal, and (Z)-7-hexadecenal as the main component, the second component, and the third component, respectively. Further, a 3:1 mixture of (Z,Z,E)-7,11,13-hexadecatrienal and (Z,Z)-7,11-hexadecadienal has been shown to have higher attractiveness than the main component alone (W. S. Leal et al., J. Chem. Ecol. 32(1), 155-168 (2006) and T. Ando et al., J. Pestic. Sci., 33(2), 152-158 (2008)).
Several preparation methods for synthesizing the sex pheromone substance (Z,Z,E)-7,11,13-hexadecatrienal have been reported. For example, it has been reported (W. S. Leal et al., J. Chem. Ecol. 32(1), 155-168 (2006)) that the sex pheromone substance can be obtained through a Wittig reaction between 10-(1,3-dioxan-2-yl)-(Z)-4-decenal and (Z)-2-pentenyltriphenylphosphonium bromide, followed by deprotection of acetal. It has also been reported (T. Ando et al., J. Pestic. Sci., 33(2), 152-158 (2008) and J. G. Millar et al., J. Chem. Ecol., 32(1), 169-194 (2006)) that the sex pheromone substance can be obtained through oxidation of (Z,Z,E)-7,11,13-hexadecatrienol with pyridinium chlorochromate and then separation of an isomer at 11-position by the subsequent purification with a silver nitrate column.